Semiconductor chip fabrication is a complicated process that involves a coordinated series of precise operations. These operations can be broadly characterized to include such steps as layering, patterning, etching, doping, chemical mechanical polishing (CMP), etc. It is well known that during the various steps in these operations, the surfaces, edges, bevels and notches of the semiconductor wafers become contaminated with a layer of residue comprised of particulates, organic materials, metallic impurities, and native oxides. The removal of these contaminants is a priority to semiconductor chip fabricators because the level of contamination on the wafer inversely correlates to the integrated circuit (IC) chip yield for each wafer and the overall reliability of those IC chips.
Some examples of operations that may result in unwanted wafer contamination include plasma etching (e.g., electron cyclotron resonance (ECR)) and CMP. During plasma etching, the wafer is placed in a reaction chamber and exposed to charged plasma which physically or chemically removes layers of material off the wafer surface. After the etching process is complete, a post-etch cleaning step follows whereby contaminant residue deposited on the wafer during the etching process is removed. Typically, this involves the application of chemistry to the front and back surfaces of the wafer followed by rinsing and drying. When using the optimal chemistry and tool settings, this post-etch cleaning step significantly removes or reduces the amount of post-etch contaminant residue on the wafer.
However, one type of post-etch residue that does not readily lend itself to removal by conventional post-etch chemical-based cleaning methods is organic polymer residue found on the wafer bevel edge, notch, and the portion of the backside of the wafer that overhangs the electrostatic chuck of the etch reactor system. This polymer residue is relatively inert and is not soluble in most known wafer-compatible chemicals. As semiconductor fabricators look towards shrinking the edge exclusion zone of the semiconductor wafer to increase the wafer's IC chip yield, it is becoming increasingly important to remove this type of residue.
Today, mechanical cleaning tools such as brush scrubbers and bevel edge cleaning wheels are used to remove polymer residue from the wafer. One system configuration may include the use of a plurality of rollers to hold and rotate the wafer, a double-sided scrubber that simultaneously scrubs the front and back surfaces of the wafer, and a bevel edge cleaning wheel that cleans the bevel edge of the wafer. Brush scrubbers are mechanically rotating brushes that scrub the top and back surfaces of the wafer to remove the polymer residue. Brush scrubbing is effective at removing the contaminants and certain types of residue on the front and back side of the wafer but is not effective at removing the polymer residue attached to the wafer bevel edge and notch.
A bevel edge cleaning wheel cleans the bevel edge of the wafer by using an abrasive wheel that rotates at a different tangential velocity than the wafer to mechanically sheer off the contaminant residue at the point of contact between the wafer bevel edge and the wheel. The difficulty with using a bevel edge cleaning wheel is that it requires an abrasive incorporated into the wheel material, which becomes worn with repeated use and therefore requires frequent replacement. Additionally, contaminant particles that are loaded onto the abrasive wheel during cleaning can become dislodged and end up as defects on the wafer. Likewise, all of the above methods and tools fail to clean the wafer notch. These shortcomings with the current methods and tools may cause greater process downtime for equipment maintenance, reduced fabrication process throughput, and decreased IC chip yield for each wafer.
In view of the forgoing, there is a need for a cleaning apparatus that avoids the problems of the prior art by allowing for the cleaning of both the bevel edge and notch of the semiconductor wafer. Further, there is a need for a bevel edge cleaning device that will not require frequent replacement and will not result in residue particles being dislodged onto the wafer during cleaning.